United lost the first-leg last night 2-0 in Athens.
"It's the worst we've played in Europe [this season], that's for sure," said Moyes in his post-match press conference.
"It was a really poor performance. We didn't get going from the start. We didn't deserve anything from tonight.
"We just never got to grips with things. To a man, you could hardly pick anyone out [who played well]. We just didn't perform well.
"I'm surprised. I didn't see that level of performance coming. We came into the game in good form and a good mindset but it didn't show tonight.
"I have to say I don't think we were two goals worse off in the game. [For the first goal] they had a shot, which got deflected... but we didn't offer enough on the night to create a goal really."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball